Bi and Sb are completely soluble in each other in both liquid and solid phases. The melting point

of pure $Bi$ is $271C$ and the melting point of pure $Sb$ is $631C.(15\%)$

$(1)$ Draw the Bi$-$Sb binary phase diagram. Then indicate the phase$($s$)$ and degree of freedom in

each region in the phase diagram. $(10\%)$

$(2)$ An alloy with a composition of $40wt\%Bi-60wt.\%Sb$ is slowly cooled from liquid to solid.

Based on your drawing, give the composition of the solid phase first formed and the

composition of the liquid phase last disappeared during cooling. $(5\%)$